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'Single line components' in the hoisting and braking systems of offshore cranes

  • Safety notice: 2/2005
  • Issue date: Feb 2005

Introduction

1. A serious incident has occurred which involved the uncontrolled lowering of a crane boom. This notice describes the incident and outlines the actions that should be taken.

2. Many offshore cranes, particularly older cranes, may have hoisting and braking systems that contain 'single line components'; the failure of one such component will result in the failure of the system. This failure will almost always result in the uncontrolled lowering of the boom and/or the load. It is therefore essential to ensure any such components are identified and that the maintenance and inspection philosophy, together with the maintenance and inspection activities undertaken, are sufficiently robust to ensure the continued integrity of these systems.

Background

3. An incident occurred on a Stothert & Pitt OS200 M1 diesel hydraulic pedestal crane that was installed in 1980. The offloading of a supply boat had just commenced and the first load to be lifted comprised of a small 1.8 tonne mini container. As this container was being lifted up and onto the installation a loud bang was heard. The crane boom immediately started to lower in an uncontrolled manner accompanied by screeching and rumbling noises. The falling boom struck two turbine exhausts stacks, damaged a walkway, and came to rest hanging vertically down from the boom hinge pins, with the boom tip in the sea. There were no injuries sustained by the people involved in the lifting operation. However the incident could have resulted in serious injuries or fatalities.

4. The winch units for both the crane main hoist and boom hoist comprised of a hydraulic motor driving a large reduction gearbox. The system of winch braking comprised of a multi-disc brake mounted on the power input side of the gearbox. The output shaft from the gearbox had an external spline that mated to an internal spline on a bossed ring bolted onto the side of the hoist winch drum.

5. Examination of the boom hoist winch revealed that a catastrophic failure had occurred at the splined connection between the gearbox output shaft and the splined boss ring on the winch drum. With the brake mounted on the winch gearbox input shaft, the gearbox and the winch drum to gearbox connection became single line components in the boom hoisting system; the failure of either of these components would result in the uncontrolled lowering of the boom.

6. Failure had occurred through extensive and excessive degradation of the splines, which over a period of time had worn the splines until a point was reached where the remaining contact area was unable to withstand the applied loading.

7. The inspection routine in place at the time of the incident did not include the withdrawal and full visual examination of both male and female splines, therefore the extent of the degradation of the splines was not known.

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Actions required

8. With guidance from the crane manufacturer or a competent person, dutyholders should;

  1. review the design of their cranes to ensure they have identified whether any single line components exist in hoisting and braking systems. Techniques such as 'failure mode effects analysis' should be employed;
  2. where such components are identified, ensure that the maintenance and inspection activities undertaken on these components are sufficient in terms of frequency and scope, to ensure that any deterioration is identified and the appropriate corrective action is undertaken;
  3. in the longer term, where such single line components are identified, consider the practicability of any modifications that will result in their elimination;
  4. verify that the 'competent person' who undertakes the 'thorough examination' of the crane thoroughly examines the hoisting and braking systems and where they consider it appropriate, any components that form such systems;
  5. discuss the details of the thorough examination of the hoisting and braking systems with the competent person. The competent person may require the opening up of concealed or encased parts by a skilled person at the time of the thorough examination, or alternatively will require evidence that such internal examinations have been undertaken and then review the results of such examinations;
  6. ensure the scope of the thorough examination, the scope of the inspection scheme and the maintenance activities relating to all hoisting and braking systems (eg testing, inspection, component replacement intervals etc) continue to be appropriate as the age of the crane increases; and
  7. in the case of winch unit transmission systems that are the same as (or of a similar configuration to) the Stothert & Pitt OS200 M1 Crane, the wear between the gearbox output splined shaft and the mating drum hub boss should be inspected at intervals specified by the crane manufacturer or a competent person. The crane manufacturer or the competent person should be consulted about acceptability or otherwise of these readings. Care should be taken to ensure the correct alignment of mating parts on re-assembly.

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Relevant legal requirements

9. The relevant legal requirements are:

References

10. You can find additional information in the following publications:

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Further information

11. Any queries relating to this safety notice should be addressed to:

Health and Safety Executive
Hazardous Installations Directorate
Offshore Division
Lord Cullen House
Fraser Place
Aberdeen
AB25 3UB

Tel: 01224 252500
Fax: 01224 252615

This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice

Updated 2009-09-06